E. Haines and J. Wallace, "Shaft Culling for Efficient Ray-Traced Radiosity," Eurographics Workshop on Rendering, E. Jansen, ed., Springer-Verlang, Berlin, May  Home/Search   Document Not in Database   Summary   Related Articles   Check

....points [8] Casting more rays normally results in a more accurate estimate of the visibility, but there are no error bounds on the resulting approximation. Many schemes for accelerating visibility computations in radiosity were proposed by researchers over the years. These include shaft culling [7], global visibility preprocessing [15] backprojections [2] and the visibility skeleton [3] Sillion and Drettakis [12, 14, 13] represent the scene by a hierarchy of clusters. Each cluster is treated as an isotropic attenuating volume, allowing to approximate quantitative visibility queries very ....

E. A. Haines and J. R. Wallace. Shaft culling for efficient ray-traced radiosity. In Proceedings of the Second Eurographics Workshop on Rendering (Barcelona, Spain, May 13--15, 1991.

....parallel horizontal edges, one of and one of and supports from above. In general, there are two such planes. Let # be the plane that supports from below. The shaft is the area bounded by #, #, ## , ## , #,and# . Notice that our definition of a shaft is different from that in [13]. Observation 1 implies that there exists a visibility ray between inside the shaft only if there exists a visibility ray on the ceiling of ##. More precisely, let # # denote the point # #,andlet# # denote the point # #. Similarly, # is denoted by # # ,and# # is ....

A. E. Haines and J. R. Wallace. Shaft culling for efficient ray-traced radiosity. 2nd Eurographics Workshop on Rendering, pages 122--138, 1994.

....two patches. It is typically estimated by shooting rays between the two patches, and counting the percentage of rays blocked by occluders. The hierarchical representation with links can be adapted to allow fast radiosity modification [DS97] by augmenting the links with a shaft data structure [HW91] In addition, previously subdivided links, called passive links are maintained. The passive links contain all the necessary information allowing them to be reactivated at no cost, if it is required by a geometry change. SeeFigure3foranexample. a) b) c) Figure 3: a) Original subdivision and ....

Eric Haines and John Wallace. Shaft culling for efficient ray-traced radiosity. In Eurographics Workshop on Rendering, 1991.

....into a shaft, which we call a fat line or fat ray (Fig. 4(a) This shaft is the cylinder defined by the spheres of any two points centered on the line. A vertex is a sphere of radius #, which we will call a fat vertex, Fig. 4(b) and an edge is a cylindrical shaft (similar in spirit to that of [12]) between the two spheres of its extremal vertices, which we will call a fat edge, Fig. 4(c) Since faces are only considered as blockers in the context of our approach, they remain as is. There are five kinds of interactions between a line and a face, shown in Fig. 5. The first two cases, ....

E. A. Haines. Shaft culling for efficient ray-traced radiosity. In Photorealistic Rendering in Comp. Graphics, pages 122--138. Springer Verlag, 1993.

....are possible. First, there are really only three distinct depths, for the background, source, and blocker which can be discretely represented. More significantly, only source vertices and vertices which otherwise appear inside the source need be traced. Performance can be improved by shaft culling [11] the scene against the source and only tracing unculled polygons. Additionally the entire scene need not be clipped on the viewing plane only the source polygon need be clipped. 4.2 Radiosity and Subdivided Environments In radiosity systems the intrinsic scene polygons are subdivided into many ....

Eric Haines and John Wallace. Shaft culling for efficient ray-traced radiosity. In Eurographics Workshop on Rendering, 1991.

....and are intersected in parallel with the given ray. A downward min scan on the computed intersection distance gives the closest object intersected by a given ray. Our technique of generating candidate sets is not unlike the shaft culling technique introduced recently by Haines and Wallace [19]. They consider ray casting in the context of radiosity form factor estimation. Candidate lists are comprised of all objects overlapping the the convex hull of an origin and destination object. This technique requires that for each ray an origin and destination object is known, as is the case in ....

Haines, E. A., and Wallace, J. R. Shaft Culling for Efficient Ray-Traced Radiosity. In Proceedings of Second Eurographics Workshop on Rendering (Barcelona, Spain, May 1991), Eurographics, Springer Verlag. Also published in Siggraph 91 course notes: Frontiers of Rendering.

....of detecting local discontinuities arising from cases 1 6. Case 1: Occluders. There could be occluding objects between the extremal rays, as shown in Figure 4 3, so that ray R intersects a different object than the extremal rays. These occluders are detected using a variant of shaft culling [HW91, TBD96] Bounding boxes are constructed around the source of the extremal rays and the destination of the extremal rays. A shaft is constructed between these two bounding boxes, and the bounding boxes of all objects in the scene are intersected with this shaft. If the bounding box of any object ....

....while guaranteeing correct results. To guarantee that the correct visible surface is found for each pixel, the reprojection algorithm conservatively determines visibility by suppressing the reprojection of linetree cells that might be occluded. This occlusion is detected by shaft culling [HW91] each clipped back face against the current viewpoint. The shaft consists of five planes: four planes extend from the eye to each of the edges of the clipped back face, and the fifth back plane is the plane of the back face of the linetree cell. If any object intersects the shaft, the ....

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E. Haines and J. Wallace. Shaft culling for efficient ray-traced radiosity. In Proc. 2nd Eurographics Workshop on Rendering, May 1991.

....5 depicts seven of the sixteen extreme rays through a pair of squares. Observe that the set of rays through a pair of convex objects, although convex in 4D rayspace, has an hourglass nature in 3D; when considered only inside the convex hull of the objects, this set has been called a shaft [12]. 6.2 Radiance Interpolation We now have a mechanism by which all rays through some volume of space can be represented, and by which a sample or query ray can be checked for inclusion in a represented set. However, rays spawned by a ray tracing algorithm not only have geometric attributes, but ....

....of the region s extremal ray trees. 6.3.2 Detecting Blockers A B C B B C C A A ( a ) b ) c ) Figure 6: Establishing the absence (a) or potential presence (b, c) of blockers. Detecting blockers is slightly more involved. To do so, we employ a dynamic version of shaft culling [12], which was originally developed for use in a radiosity algorithm based on ray casting. The pseudocode of x2 invokes Intersect( to determine the first intersection of a spawned ray with a scene object. For efficiency, Intersect( is implemented as a query on a hierarchical spatial partition [10] ....

Haines, E., and Wallace, J. Shaft Culling for Efficient Ray-Traced Radiosity. In Proc. 2 nd Eurographics Workshop on Rendering (May 1991).

....is somewhat dated. Several researchers have developed algorithms for computing accurate direct illumination. Teller [26] showed how to compute antiumbras and antipenumbras. Lischinski [19] introduced discontinuity meshing to produce global illumination solutions with accurate soft shadows. Haines [15] introduced shaft culling to speed up visibility computation in radiosity systems. Durand et al. 10] create a mesh of all illumination discontinuity events; this mesh can be used to compute illumination due to area light sources. Stark et al. 25] use splines to represent shadow irradiance in ....

Eric A. Haines and John R. Wallace. Shaft culling for efficient ray-traced radiosity. In Photorealistic Rendering in Computer Graphics (Proceedings of the Second Eurographics Workshop on Rendering), New York, 1994. Springer-Verlag.

....As the number of samples increases, the probability of missing a contributing blocker or emitter decreases. Section 4.3.2 describes how additional samples are automatically acquired so that blocker lists converge over time. An alternative technique to determine blocker lists is shaft culling [14]. Shaft culling produces conservative blocker lists by finding all potential blockers that lie in a shaft from the patch to the emitter. However, shaft culling is too conservative; for example, in Figure 2, shaft culling would probably include all the faces of the cube in the blocker list for ....

E. Haines and J. Wallace. Shaft culling for efficient ray-traced radiosity. In Proc. # ## Eurographics Workshop on Rendering, May 1991.

....creating complete discontinuity mesh, that encodes all visual events involving a light source. Classical global illumination algorithms based on radiosity method evaluate form factors between two patches (or regions) 150] The visibility determination is a crucial step in form factor evaluation [188, 86, 187, 127, 184]. Similar visibility determination takes place in the scope hierarchical radiosity algorithms [166, 56, 48] Certain VFP problems that determine visibility over a period of time can be transformed to a corresponding static VFR problem. This transformation can be particularly useful for ....

E. A. Haines and J. R. Wallace. Shaft culling for efficient ray-traced radiosity. In P. Brunet and F. W. Jansen, editors, Photorealistic Rendering in Computer Graphics (Proceedings of the Second Eurographics Workshop on Rendering), New York, NY, 1994. SpringerVerlag. also available via FTP from princeton.edu:/pub/Graphics/Papers.

....between two patches. It is typically estimated by shooting rays between the two patches, and counting the percentage of rays blocked by occluders. The hierarchical representation with links can be adapted to allow fast radiosity modification [9] by augmenting the links with a shaft data structure [14]. In addition, previously subdivided links, called passive links are maintained. The passive links contain all the necessary information allowing them to be reactivated at no cost, if it is required by a geometry change. See Figure 3 for an example. a) b) c) Figure 3: a) Original subdivision ....

Eric Haines and John Wallace. Shaft culling for efficient raytraced radiosity. In P. Brunet and F.W. Jansen, editors, Photorealistic Rendering Techniques in Computer Graphics (2nd EG Workshop on Rendering), pages 122--138. Springer Verlag, 1991. Held in Barcelona, Spain.

....a regular subdivision patter is used. Figure 3 shows a visualization of the initial situation and two examples for subdivided links. If there is no occluder between the two nodes, a link is stored. Otherwise the larger node is subdivided and the process is applied recursively. Shaft culling [12] is used to speed the refinement process. Note that shaft culling can be optimized in the recursive refinement by temporarily storing the current list of potential occluders during recursive subdivision and using this list during further refinement of the link [1] 7] For each link created the ....

Haines, E. A., "Shaft Culling for Efficient RayTraced Radiosity", In Brunet and Jansen, editors, Photorealistic Rendering in Computer Graphics, Springer Verlag, pp. 122-138, 1993.

....using an appropriate object representation for non planar surfaces, we also achieve significant savings and better quality. Finally, when modifying a scene dynamically, we limit the amount of recomputation. We discuss all of these improvements next. Visibility classification. We use shaft culling [9] for visibility classification in our approach. For a given link, we determine the list of potential blockers across the link. Bounding boxes are opened at the first level if they overlap the shaft, bounding boxes outside the shaft are removed from the list and bounding boxes entirely contained in ....

E. A. Haines and J. R. Wallace. Shaft culling for efficient ray-traced radiosity. 2nd EG Workshop on Rendering (Photorealistic Rendering in Computer Graphics), 1994.

....of rays and geometry were processed in order based on how many rays were contained within. Rays in voxels were processed as a group so that candidate objects for intersection tests could be found and so that the overhead of octree traversal could be reduced. In a manner similar to shaft culling[9], Reinhard and Jansen gathered rays with common origins into frustums that were traced together so that a set of the objects inside the frustum could be found to accelerate ray object intersection tests[18] Pharr and Hanrahan reordered eye rays using space filling curves over the image plane to ....

Eric Haines and John Wallace. Shaft culling for efficient raytraced radiosity. In Eurographics Workshop on Rendering, 1991.

....can be missed, causing flickering edges, or shadow movements can leave stains. On the other hand we can expect visibility not to depend on time for a large number of links (e.g. between nearby surfaces that do not move or that have the same movement) As a consequence, we decided to use shafts [11] to detect moving surfaces stepping between the two nodes of a given link, to be able to force an appropriate subdivision. 1. If both the source and the receiver of the considered link share the same movement, we build the shaft joining their bounding boxes. Then we hierarchically test for ....

Eric Haines and John Wallace. Shaft culling for efficient ray-traced radiosity. In Eurographics Workshop on Rendering, 1991.

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E. Haines and J. Wallace, "Shaft Culling for Efficient Ray-Traced Radiosity," Eurographics Workshop on Rendering, E. Jansen, ed., Springer-Verlang, Berlin, May

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Eric Haines and John Wallace. Shaft Culling for Efficient Ray-Traced Radiosity. In Eurographics Workshop on Rendering, 1991.

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E. Haines and J. Wallace. Shaft culling for efficient ray-traced radiosity. In Eurographics Workshop on Rendering, 1991.

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E.A. Haines and J.R. Wallace. Shaft culling for efficient ray-traced radiosity. In Eurographics Workshop on Rendering, pages 122--138, June 1991.

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Eric A. Haines and John R. Wallace. Shaft Culling for Efficient RayTraced Radiosity. In P. Brunet and F. W. Jansen, editors, Photorealistic Rendering in Computer Graphics (Proceedings of the Second Eurographics Workshop on Rendering), New York, NY, 1994. SpringerVerlag.

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E. Haines and J. Wallace. Shaft culling for efficient raytraced radiosity. In Eurographics Workshop on Rendering, pages 122--138, 1991. 3

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Haines EA, Wallace JR. Shaft culling for efficient raytraced radiosity. In Photorealistic Rendering in Computer Graphics (Proceedings of the Second Eurographics Workshop on Rendering), Brunet P, Jansen FW (eds). Springer: New York, 1994.

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Haines, Eric A., and John R. Wallace. "Shaft Culling for Efficient Ray-Traced Radiosity." Second Eurographics Workshop on Rendering, May 1991, p. ?. f75g

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E. A. Haines and J. R. Wallace. Shaft Culling for Efficient Ray-traced Radiosity. In P. Brunet and F. W. Jansen, editors, Photorealistic Rendering in Computer Graphics (Proceedings of the 2nd Eurographics Workshop on Rendering), New York, Springer-Verlag, pp. 122--138, 1994.

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